1. Field of the Invention
This invention relates to a phenolic chelate resin comprising the three-dimensional product obtained by cross-linking a specific phenolic compound with a phenol and an aldehyde. This invention further relates to a method of adsorption treatment which comprises selectively adsorbing ferric ion and/or cupric ion in an aqueous solution using such a resin.
2. Description of the Prior Art
Various studies have been made and many articles have been reported on chelate resins comprising a polymeric material with a ligand capable of forming a complex with a heavy metal ion incorporated into the polymeric material. For example, U.S. Pat. No. 3,936,399 discloses the use of a phenol-formaldehyde resin as a resin base and U.S. Pat. No. 2,910,445 discloses the use of polystyrene as a resin base. Further, examples of such resins which are now commercially available include "Dowex A-1" (tradename, produced by Dow Chemical), "Diaion CR-10 and 20" (tradename, produced by Mitsubishi Chemicals) and "Unicellex UR-10, 20 and 30" (tradenames, produced by Unitika). These resins are useful as agents for removing heavy metal ions through adsorption as well as heavy metal recovering agents. These chelate resins have been found generally effective for removing heavy metals such as copper, nickel and zinc by adsorption from an aqueous solution as well as for recovering such metals from the aqueous solution. However, all these conventional chelate resins are essentially of the iminodiacetic acid type having one iminodiacetic acid per phenyl nucleus incorporated as a ligand in the resin, and therefore, their ability to selectively adsorb and remove a plurality of heavy metal ions, particularly, ferric ion and/or cupric ion is low. Also, their ability to selectively trap heavy metal ions such as ferric ion and/or cupric ion in an aqueous solution of a low pH is low.
It is known that phenols easily form complex salts with ferric ions and that ethylenediaminetetraacetic acid (EDTA) is a good low molecular weight chelating agent. Schwarzenbach et. al. [Helv. Chim. Acta. 35, 1785 (1952)] synthesized an EDTA-analogous chelating agent, i.e., p-substituted (1-hydroxy-phenylene-2,6)-bis-methyl iminodiacetic acid that is in some respects similar to the phenolic compound which is used in this invention. It is difficult, however, to make a resin of this compound. Although phenolic chelate resins are not particularly novel as chelate resins, those described in prior art references, for example, U.S. Pat. No. 3,936,399 and Japanese Patent Application (OPI) No. 51,389/74 still have the defects mentioned above because the chelating groups present are of the iminodiacetic acid type described above or are of the aminocarboxylic acid type.
A variety of aqueous solutions that contain heavy metals exist. If it becomes possible to selectively adsorb ferric ions and/or cupric ions and remove them from an aqueous solution containing a plurality of heavy metal ions so as to recover them separately, the aqueous solution thus treated can be reused without any special treatment. However, conventional chelate resins do not have a high selective adsorbability for ferric ions and/or cupric ions, nor do they have high selective adsorbability for these ions in an acidic aqueous solution at a pH of about 3 or less.